Sheet type fin antenna having loop fed excitation



Nov. 1, 1966 Filed Aug. 26, 1963 c. w. s'rUcKEY, JR., ETAL 3,283,327 SHEET TYPE FIN ANTENNA HAVING LOOP FED EXCITATION 2 Sheets-Sheet 1 NOvl, 1956 c.w.s1'ucKEY,JR., ETAL 3,283,327

SHEET TYPE FIN ANTENNA HAVING LOOP FED EXCITATION Filed Aug. 26, 1963 2 Sheets-Sheet 2 United States Patent O 3,283,327 SHEET TYPE FIN ANTENNA HAVING LOOP FED EXCITATION Clarence W. Stuckey, Jr., Tarzana, and Robert A. Meyers, Torrance, Calif., assignors to Stoddart A11-craft Radio, Inc., Los Angeles, Calif., a corporation of California Filed Aug. 26, 1963, Ser. No. 304,367 Claims. (Cl. 343-705) This invention relates to a radio antenna and more particularly to such an antenna that is suitable for use in an aircraft communications system.

The aircraft communication channels most generally in use are in the VHF and UHF ranges. The channels generally allocated for air to ground communications occupy a fairly broad range of frequencies within each of these spectrums. A good aircraft communications antenna for either the UHF or the VHF ranges must therefore be capable of transmitting and receiving eiiiciently over a relatively wide frequency range inl at least one of these spectrums.

An airborne communications antenna must not only have broad band characteristics, but also 4must occupy a minimum amount of space and have a shape that will result in low aerodynamic drag. The combined physical and electrical requirements for an eflicient aircraft communications antenna pose a diflicult design problem and generally result in a fairly expensive end product. In some of the designs of the prior art, the broad-banding effects have been achieved in an antenna of desirable shape and size by utilizing coaxial line matching networks and by top-loading the driven element. Many prior art antenna utilize sheet metal elements. To achieve the optimum end results in the nished product, it is necessary that the elements are fabricated to precise prel determined dimensions. This imposes somewhat of a production problem in the devices yof the prior art in that the elements utilized often comprise a somewhat complex configuration of units which must be cut and positioned precisely. With the devices of the piror art, the accurate reproduction, on a production line basis, of the prototype design is somewhat difficult and therefore tends to greatly increase the cost of the antenna.

The device of this invention overcomes the shortcomings of the prior art in providing a highly eicient yet compact antenna which is readily reproducible. This antenna has a low `standing wave ratio over an entire communications range such as the aircraft VHF or UHF bands and is shaped to be housed in a fairing having low aerodynamic drag characteristics.

'I'his end result is achieved in the device of the inven- V tion by utilizing a unique antenna conguration which is readily reproducible by etched circuit techniques. The driven element is a broad metal strip which is top loaded by means of a top loading lsection directly connected to the driven element and a series of parasitic matching sections coupled to the driven element. Proper coupling of the parasitic lsections is achieved by means of a series of resonant slots. Signals are coupled to and from the antenna by means of a strip transmission line which is etched on a separate etched circuit board, this separate etched circuit board being attached to the main etched circuit board on which the radiating elements are etched. The entire unit which is substantially at in its end configuration, is housed in a dielectric fairing having low aerodynamic drag.

It is therefore an object of this invention to provide l a broad-band aircraft communications antenna having excellent electrical and physical characteristics which is of more economic fabrication than prior art devices.

It is still another object of this invention to facilitate 3,283,327 Patented Nov. 1, 1966 fr ICC the manufacture of broad-band aircraft communications antennas.

It is still another object of this invention to provide an aircraft communications antenna having a low standing Wave ratio over a broad frequency` band which is capable of production by etched circuit techniques.

It is still a further object of this invention to provide an elcient aircraft communications antenna having a physical configuration presenting low aerodynamic drag.

Other objects of this invention will become apparent from the following descriptionv taken in connection with the accompanying drawings Iof which,

FIG. 1 is a side elevation view of a preferred embodiment of the device of the invention,

FIG. 2 is a side elevation view of the embodiment shown in FIG. 1 as viewed from the opposite side thereof,

FIG. 3 is side elevation view of the strip transmission line etched circuit board unit utilized in the device of the invention and,

FIG. 4 is a side elevation view of the strip transmission line of FIG. 3 as viewed from the opposite side thereof.

-Refern'ng now to the figures, flat etched circuit board 12 is attached to metal base plate 11 by means of angle brackets 14. Such attachments may be achieved, for example, by means of rivets 15.

Board 12 may be of a dielectric material which was originally completely copper-clad, such copper covering having been etched away by techniques well known in the art to leave the configuration shown in FIG. l. A copper radiating element comprising directly excited elements and parasitic elements is thus etched out onboard 12. The radiating element comprises relatively broad strip section 18, substantially horizontal top-loading strip section 19, and parasitic elements 21, 22, 23, and 24. Proper matching of the parasitic elements is achieved by means of resonant slots 25, 27, 29, 30, 31, 35, and 36.

In an operative embodiment of the device of the invention for utilization over the entire VHF aircraft communications range (116-152 megacycles), the following dimensions for the various elements as appropriately identified in FIG. 1 are utilized. In this embodiment, the standing wave ratio was found to be less than 2:1 over the entire range. The dimensions given are in portions of a wavelength at the center of the frequency range covered. Base plate l11 establishes the horizontal reference plane.

a (The vertical extent of driven elements 18 and 19 above base plate 11) wavelength 0.1.3 c (The width of strip element 18) do 0.042 e (The vertical distance of the bottom of parasitic element 24 from the top of section 19) Wavelength 0.07 (The vertical distance between the top of section 19 and the bottom of parasitic element 21) wavelength 0.051 g (The vertical distance between the top of section 19 and the bottom of parasitic element 23) wavelength 0.045 h (The vertical distance between the top of section 19 and the edge of the bottom portion of this section) wavelength-- 0.037 d (The total distance between the ends of slots 25 and 27) wavelength 0.09 j (The total length of slot 31) do 0.09 k (The perpendicular distance from the edge of slot 29 to the edge of circuit board 12) wavelength- 0.035 m (The width of slot 29) do 0;01 .Angle q degrees 58 Angle n 122 The dimensions for the various slots are given for a circuit board fabricated of a material having a dielectric constant such that the velocity of radio waves therein is one half that of their free space velocity. The effective electrical lengths, of these slots for the radio frequency signals involved is therefore twice the physical dimension indicated.

The antenna unit is housed in a fairing 40 having low aerodynamic drag characteristics. Fairing 40=may be fabricated of a dielectric material such as fiberglass and is attached torbase plate 11 by any suitable means.

Radio signals are coupled to and from the antenna by means of a transmission line unit 42 which is a separate flat etched circuit board appropriately etched on both sides thereof. Transmission line unit `42 is coupled to the radio receiver and transmitter through coaxial connector 43. Transmission line unit 42 is fixedly attached as shown in FIG. 2 to the side of etched circuit board 12 opposite the side thereof having the radiating elements thereon. Such attachment is -achieved by means of rivets 44.

The details of transmission line unit 42 are best shown in FIGS. 3 and 4. The inner side of transmission line unit 42, i.e. the side abutting against the surface of board 12, is etched to leave an open loop shaped conductive strip 47 thereon. One end of conductive strip 47 is attached to the center portion of coaxial connector 43. The other end of this strip is grounded to `base plate 11 at point 48. The portion of strip 47 between connector 43 and point 50 operating in conjunction with broad strip 55 which is connected to radiating element 18 at point 60, forms a series matching line which `operates as a transformer to couple RF energy to the radiating element. The radiating element is maintained at D.C. ground potential while a proper input impedance is reflected at connector 43 at the signal frequencies. The portion of strip 47 between points 50 and 48 forms a grounded shunt line which operates in conjunction with the series matching line to efficiently couple RF energy to the radiating element.

Broad conductive strip 55 which is etched out on the outer side of transmission line unit 42, is a grounded parallel plate which provides one side of the transmission line formed by the series matching line portion of strip 47.` 'Ihe bottom end of panallel plate element 55 is attached to base plate 11 by means of rivets 56. The top end of plate 55 is riveted to the radiating element 18 at point 60 to provide a D.C. ground for protection against lightning.

A reactive slot matching network 63 is coupled to the grounded shunt line portion of strip 47 to effectively add series capacitance to the line andrthereby improve the standing wave ratio at certain portions of the operating band.

The device of this invention thus provides a simple yet lhighly efficient aircraft communications antenna which is readily reproducible and which can easily be contained Within a fairing having low aerodynamic drag. The basic design illustrated may be utilized, for example, over any such broad-band, such as covered by the aircraft communications and navigations channels in the VHF or UHF ranges.

While the device of the invention has been described and illustrated in detail, it is to be clearly understood that this is intended -by way of illustration and example only and is not to -be taken by way of limitation, the spirit and scope of this invention being limited only by the terms of the following claims.

We claim:

1. An aircraft communications antenna comprising -a base plate,

a first fiat etched circuit board fixedly attached to said base plate, the broad surfaces of said etched circuit board lying in planes substantially normal to the broad surfaces of said base plate, said etched circuit board having a driven element and a plurality of parasitic matching elements etched thereon, said parasitic elements being coupled to said driven element,

a second at etched circuit board fixedly attached to said first board, a strip transmission line being etched on said second board, said strip transmission line being connected to said driven element, said transmission line including a thin strip forming an open loop etched on one side of said second board and a broad strip etched on the other side of said second board, and

connector means for coupling radio signals to and from said strip transmission line.

2. In a radio antenna a base plate,

a first etched circuit board fixedly yattached to said base plate, the broad surfaces of said first board being substantially normal to the broad surfaces of said base plate, said first circuit board having antenna radiating elements etched on one of the `broad surfaces thereof, said radiating elements including a first broad strip forming a driven element section, said broad strip running from said base plate along an axis forming an acute angle with the broad surfaces of said base plate, a second strip running along an axis substantially parallel to said base plate and integrally joined to said first strip at the `portion thereof farthest from said base plate, and a plurality of parasitic elements positioned adjacent to said radiating elements and to each other, said parasitic elements being located between said second strip and said base plate and opposite said broad strip,

a second etched circuit 4board .having a thin strip forming an open loop etched on one side thereof and a relatively broad strip etched on the opposite side thereof, one of the ends of said thin strip and one of the ends of said broad strip being attached to. said base plate, the other end of said broad strip being attached to said driven element section of said first board, and

a coaxial connector having outer and innerconductors, the outer conductor of said connector being attached to said base plate, the inner conductor ofsaid connector being attached to the other of the ends of said thin strip.

3. The antenna as recited in claim 2 wherein said first broad strip runs from said base plate along an axis forming an acute angle with the broad surfaces of said base plate of between 55 and 60 vdegrees and the top edge of said second strip is a distance of substantially .13 wavelength, at the center operating frequency of said antenna, from said base plate.

4. The antenna as recited in claim 2 wherein said first broad strip is of a width of substantially .042 wavelength at the center operating frequency of said antenna.

5. In a radio `antenna a base plate,

a first etched lcircuit board fixedly attached to said base plategtthe broad surfaces -of said first board being substantially normal to the broad surfaces of said base plate, said first circuit board having antenna radiating elements etched on one of the broad surfaces thereof,

a second etched circuit board having a thin strip Iforming an open loop etched on one sidethereof and a relatively broad strip `etched on the opposite side thereof, one of the ends of said thin strip and one of the ends of said broad strip being attached to said base plate, the other end of said broad strip being :attached to said driven element section of said first board, and` a coaxial connector having outer and inner conductors, the outer conductor of said ,connector being attached to said base plate, the inner conductor of said connector being attached to the other of the ends of said thin strip.

6. The antenna as recited in claim 5 wherein said one side of said second etched circuit board abuts against the other of the broad surfaces of said first etched circuit board.

7. In a radio antenna,

a base plate,

a irst etched circuit board iixedly attached to said base plate, the broad surfaces of said board being substantially normal to the broad surfaces of said base plate,

said first etched circuit board having a conductive driven element etched on one surface thereof, said iirst etched circuit board further having a plurality of parasitic elements etched on said one surface thereof, said parasitic elements being positioned between the top of said driven element and said base plate, said parasitic element-s being separated from each other and from said driven element by a plurality of reslonant slots.

a second etched circuit board, said second circuit board having a thin conductive strip etched on one surface thereof, said thin strip forming an open loop, and la broad longitudinal strip etched on the opposite surface thereof, the bottom por-tion of said broad longitudinal strip being attached to said base plate, said second board being attached to said first board with said one surface thereof abutting 'against the surface lof said first board opposite the surface on which said conductive elements are etched, one Of the ends of said thin strip being attached to said base plate, said board longitudinal strip in said second board being attached to the driven element of said first board, and

means for connecting the other of the ends of said thin strip to a radio transmitter and receiver.

8. The antenna as recited in claim 7 wherein fthe extreme top portion of said driven ele-ment is substantially .13

Wavelength, at the center operating frequency of said 4 antenna, from said base plate.

9. In a radio antenna, a base plate, a first etched circuit board xedly attached to said base plate, the broad surfaces of said board being sub- 45 stantially normal to the broad surfaces of said base plate,

said first etched circuit board having a conductive driven element etched on one surface thereof, said driven element including a broad strip section running along an axis forming an acute ,angle with said base plate and `a top loading section running in a direction substantially parallel to said base plate, said first etched 5 circuit board further having a plurality of parasitic elements etched on said one surface thereof, said parasitic elements being .positioned between said top loading section and said base plate, said parasitic elements being separated from each other and from said driven element by a plurality of resonant slots,

a second etched circuit board, said second circuit board having a thin conductive strip etched Ion one surface thereof, said thin strip forming an open loop, and a broad longitudinal strip etched on the opposite surface thereof, the bottom portion of said broad longitudinal strip being attached to said base plate, said second board being attached to said first board with said one surface thereof abutting :against the surface of said first board opposite the surface on which said conductive elements are etched, one of the ends of said thin strip being attached to said base plate, said broad longitudinal strip on said second board being attached to the driven element of said first board, and

a coaxial connector having inner and outer sections, the outer section of said connector being attached to said base plate, the inner section of said connector being attached to the other of the ends of said thin strip.

10. The antenna Ias recited in claim 9 wherein said 30 broad strip section of said lirst etched circuit board has a width of substantially .042 Wavelength, at the center operating frequency -of -said antenna, and said parasitic ele-ments extend substantially .07 Wavelength, at the center operating frequency -of said antenna from the top edge of 35 said top 4loading section.

References Cited by the Examiner UNITED STATES PATENTS 0 2,614,219 10/1952 Cary 343--845 2,661,442 12/ 1953 Johnson et al. 343-708 2,994,876 8/ 1961 Josephson 343-831 OTHER REFERENCES Iosephson: Microstrip Design for Aircraft Antenna, Electrical Manufactming, vol. 62, August 1958, page 11.

HERMAN KARL SAALBACH, Primary Examiner.

G. TABAK, M. NUSSBAUM, Assistant Examiners. 

1. AN AIRCRAFT COMMUNICATIONS ANTENNA COMPRISING A BASE PLATE, A FRIST FLAT ETCHED CIRCUIT BOARD FIXEDLY ATTACHED TO SAID BASE PLATE, THE BROAD SURFACES OF SAID ETCHED CIRCUIT BOARD LYING IN PLANES SUBSTANTIALLY NORMAL TO THE BROAD SURFACES OF SAID BASE PLATE, SAID ETCHED CIRCUIT BOARD HAVING A DRIVEN ELEMENT AND A PLURALITY OF PARASITIC MATCHING ELEMENTS ETCHED THEREON, SAID PARASITIC ELEMENTS BEING COUPLED TO SAID DRIVEN ELEMENT, A SECOND FLAT ETCHED CIRCUIT BOARD FIXEDLY ATTACHED TO SAID FIRST BOARD, A STRIP TRANSMISSION LINE BEING ETCHED ON SAID SECOND BOARD, SAID STRIP TRANSMISSION LINE BEING CONNECTED TO SAID DRIVEN ELEMENT, SAID TRANSMISSION LINE INCLUDING A THIN STRIP FORMING AN OPEN LOOP ETCHED ON ONE SIDE OF SAID SECOND BOARD AND A BROAD STRIP ETCHED ON THE OTHER SIDE OF SAID SECOND BOARD, AND CONNECTOR MEANS FOR COUPLING RADIO SIGNALS TO AND FROM SAID STRIP TRANSMISSION LINE. 